Stair treads are the weight-bearing portion the make up the generally horizontally planar portion of each step on a flight of stairs. Various stair tread structures have been tried, including the following:
U.S. Pat. No. 1,778,333 discloses the manufacture of rough lumber into finished lumber with less waste for flooring, siding, and other finished lumber. This is accomplished by cutting out defects and by splitting the boards along their length to use rough lumber to provide double the quantity of finished lumber having clear wearing surfaces. Pieces of such lumber can be joined end-to-end, as the reference states that glued joints can be made as strong as required.
U.S. Pat. No. 4,730,425 discloses a returned stair tread for use on an open portion of a stairway having a return nosing joined on at least one side edge to form an exposed shaped or mitered joint to join the tread and the nosing. A nail, wood screw, or other fastener, or a wood adhesive, can be used to prevent sliding of the nosing and tread relative to each other. U.S. Pat. No. 5,088,247 discloses a returned stair tread of wood and a return nosing joined on a side edge. The nosing and tread are slidable relative to one another and are joined on a rear end portion with an expansion joint.
U.S. Pat. No. 5,386,673 discloses a returned stair tread having a return nose fitting flush against its side edge and being slidably interconnected by tongue and groove construction. The tread also includes a non-rigid securing means to join the nose and tread along their length while permitting each to expand and contract over a range of temperatures and humidities.
U.S. Pat. No. 5,531,048 discloses a method for manufacturing a stairway made from wood-composite materials to a stairway that appears to be solid wood by using sheets of veneer overlay scribed and trimmed at least the end portions of each tread, riser, or both and leaving the central portion uncovered.
U.S. Pat. No. 5,985,398 discloses a stair tread having the appearance and structural stability of solid hardwood treads but includes a core layer made of lamellas of lower quality wood glued laterally adjacent each other and on the top surface of which is glued lamellas made of higher quality wood that are laterally glued adjacent each other. The outer wooden member most remote from the nose is formed of a core lamella that must be unbroken in a single solid piece of lower quality wood, while the surface lamella is a single solid piece of higher quality wood.
U.S. Pat. No. 6,067,758 discloses a stair construction element including a horizontal tread part and a nosing-like riser extending vertically therefrom, where the tread and nosing-like riser form an integral element encased or coated with laminate.
U.S. Pat. No. 6,082,061 discloses a stair tread including a rigid frame encapsulated with a structural plastic material. The rigid frame can be made of steel and the plastic of polyol and isocyanate blend (i.e., a polyurethane) applied by reaction injection molding.
U.S. Pat. No. 6,115,975 discloses a stair system having an improved stair nose molding and back molding to provide a free-floating riser and free-floating tread, where the stair nose molding has a cutout with tongue to receive the grooved stair tread and a stair back molding having a groove to receive the bottom edge of the riser in sliding arrangement.
U.S. Pat. No. 6,173,540 discloses a stair tread fabricated from engineered wood product such as strand board made of wood strips, with each surface layer oriented perpendicularly to the core layers and bonded with phenolic resin or binding agents and subjected to intense heat and pressure to irreversibly bond the surface and core layers and achieve suitable stair tread strength and performance criteria. The tread is made from one inch thick structural panels using standard tools, and has a rounded, forward edge and a riser groove along its entire length.
Despite these patents, there still exists a need for more cost efficient stair treads having suitable appearance and sufficient structural integrity for use in conventional stair tread applications. The present invention satisfies this need.